The present invention relates to a rotary blower, and more particularly, to a torsion damping mechanism (“isolator”) for reducing audible noise from the blower, and especially from the timing gears.
Although the present invention may be used advantageously on many different types of blowers, regardless of the manner of input drive to the blower, the present invention is especially adapted for use with a Roots-type rotary blower that is driven by an internal combustion engine. In a typical internal combustion engine used commercially for on-highway vehicles, the torque output of the engine is not perfectly smooth and constant, but instead, is generated in response to a series of individual, discrete combustion cycles.
A typical Roots-type blower transfers volumes of air from the inlet port to the outlet port, whereas a screw compressor actually achieves internal compression of the air before delivering it to the outlet port. However, for purposes of the present invention, the blower, or compressor, generally includes a pair of rotors, which must be timed in relationship to each other, and therefore, are driven by meshed timing gears. As is now well known to those skilled in the blower art, the timing gears are potentially subject to conditions such as gear rattle and bounce.
Rotary blowers of the type to which the present invention relates (either Roots-type or screw compressor type) are also referred to as “superchargers”, because they are used to effectively supercharge the intake side of the engine. Typically, the input to an engine supercharger is a pulley and belt drive arrangement that is configured and sized such that, at any given engine speed, the amount of air being transferred into the intake manifold is greater than the instantaneous displacement of the engine, thus increasing the air pressure within the intake manifold, and increasing the power density of the engine.
Rotary blowers of either the Roots-type or the screw compressor type are characterized by the potential to generate noise. For example, Roots-type blower noise may be classified as either of two types. The first is solid borne noise caused by rotation of timing gears and rotor shaft bearings subjected to fluctuating loads (the periodic firing pulses of the engine). The noise, which may be produced by the meshed teeth of the timing gears during unloaded (non-supercharging), low-speed operation is also referred to as “gear rattle”. The second type of noise is fluid borne noise caused by fluid flow characteristics, such as rapid changes in the velocity of the fluid (i.e., the air being transferred by the supercharger). The present invention is concerned primarily with the solid borne noise caused by the meshing of the timing gears.
To minimize solid borne noise, torsion damping mechanisms (“isolators”) have been developed, which can minimize the “bounce” of the timing gears during times of relatively low speed operation, when the blower rotors are not “under load”. Such torsion damping mechanisms are also referred to as “isolators” because part of their function is to isolate the timing gears from the speed and torque fluctuations of the input to the supercharger.
One known torsion damping mechanism is shown in FIGS. 1 and 2 of the present application and includes an annular body adapted to be attached to a first input shaft driven by the engine through the pulley and belt drive arrangement. A second input shaft is drivingly connected to the first input shaft by the torsion damping mechanism through a plurality of pins that are received in arcuate slots in the body. Disposed between at least one of the pins and the body of the damping mechanism is a spring providing a resilient drive between the first and second input shafts, which attenuates or isolates torque fluctuations or torque spikes for preventing audible gear tooth rattle of the timing gears during non-supercharging, low engine speed modes of operation.
During the course of the development of a supercharger, one of the primary developmental concerns has been the durability of the torsion damping mechanism, and therefore, the ultimate service or durability life of the supercharger, in terms of the number of hours of operation, prior to any sort of supercharger component failure. Manufacturability and ease of installation are also desirable characteristics of the torsion damping mechanism to ensure, among other things, proper assembly of the supercharger.